EP0457232A1

EP0457232A1 - Improvements in the control and monitoring circuit of a conversion burner

Info

Publication number: EP0457232A1
Application number: EP91107701A
Authority: EP
Inventors: Luigi Borelli; Bruno Tagliaferro; Giuseppe Canova
Original assignee: RBL Riello Bruciatori Legnago SpA
Current assignee: RBL Riello Bruciatori Legnago SpA
Priority date: 1990-05-16
Filing date: 1991-05-13
Publication date: 1991-11-21
Also published as: IT9085571A0; IT9085571A1; IT1239691B

Abstract

The invention relates to a number of improvements in the control and monitoring circuit of a conversion burner. The invention lies in that the opening of the regulation thermostat (Ta) causes the closing of the check valve of the fuel feeder, while the electric circuit which feeds the fan driving motor, the pump and the flame control device is still on and powered. If the photoresistance (FT) detects the flame absence, the operation of the feeding circuit, of the motor and of the flame control device is inhibited. But if the photoresistance detects the flame presence for a given period (T4) after the check valve closing, a blocking contact is activacted (C2L), which cannot be manually reset and which prevents the control circuit from being reset in case the thermostat line is closed.

Description

The invention relates to a number of improvements in the control and monitoring circuit of a burner especially suited for burning liquid fuels.
It is known that burners are devices suited to perform the combustion of liquid or gaseous fuels and are essentially composed of a motor which is coaxial with a fan and a pump. In the fan inlet both the fuel coming from the pump and the air stream produced by the fan converge. So, a combustible mixture which sets aflame is created. The combustion priming is realized through a spark provided by an electric control. More particularly, when the regulation thermostat is closed, also the feeding circuit of the burner motor closes. Consequently, the fan and the pump are activated simultaneously, while an electronic circuit checks the presence or absence of light in the flame area. If there is not flame, i.e if there is not light in the area under the photoelectric cell control, then the fuel valve opens and, later, a spark is primed which primes the combustion of the fuel-air mixture.
In the normal operation of the burner, the regulation thermostat opens when it reaches its pre-set temperature, and, since the thermostat is in connection with the motor feeding circuit, also the motor feeding circuit opens. Consequently, the motor stops. Since the pump is coaxial with the motor, also the fuel feeding pump stops and, at the same time, an opening-closing valve for the fuel outlet closes, the valve being placed beyond the pump. This type of operation, which characterizes the majority of the burners for liquid fuels, causes a number of disadvantages which are pointed out thereafter.
As has already been said, when the regulation thermostat opens the motor stops, the flame extinguishes, the pump stops and also the check valve connected with the pump stops.
When the pump stops, the high-pressure (10-14 bar) compressed air bubbles, which had been previously floating inside the nozzle of the fuel near the outlet, cause the fuel to back up; since there is not an air stream, the air bubbles do not burn, but lay on the combustion head and inside the boiler.
The just mentioned phenomena cause a deposit of unburnt particles inside the combustion chamber and, as the time passes, bigger deposits are formed, which reduce the heat exchange coefficient and, consequently, the boiler efficiency.
Furthermore, the fuel check valve remains open and jams out of operation defects. When the burner restarts because the regulation thermostat closes its electric contact again, the fuel outflows because during the pre-ventilation phase the fan motor is powered and therefore also the pump is activated. The fuel outflow takes place before the priming of the spark which starts the combustion. The unburnt elements buildup inside the combustion chamber is dangerous because it can cause the boiler to burst, particularly if the user resets the circuit trying to make the burner restart after the motor has jammed up repeatedly. The aim of the present invention is to overcome the above-mentioned disadvantages.
The main aim of the invention is the realization of an improved control and monitoring circuit of the burner which can avoid leakage of fuel when the burner stops, and which can also avoid a dangerous buildup of unburnt elements in the combustion chamber.
Another proposed aim of the invention is the realization of a method for checking the fuel interception by closing the fuel feeding duct.
All above mentioned purposes and others which will be better explained hereinafter are reached through the realization of a burner fitted with a control and monitoring circuit controlled by the regulation thermostat; the circuit, according to the first claim comprises:

one or more remote controls which start the electric fan and which are connected with the regulation thermostat;
one or more components of electric circuits which control that the flame is burning;
one or more valves for intercepting the fuel coming from the fuel feeding pump,

An advantage of the invention is that the closing of the check valve takes place before the air adduction stops, and therefore while the flame is still burning; any possible fuel residual outflow is therefore burned by the flame. So, the fuel does not produce either fuel residual products or deposits buildup in the combustion chamber. It is obvious that the cleaner the combustion chamber, the better the thermal exchange between the flame and the boiler water.
Another advantage is that it is easy to troubleshoot the fuel interception system and/or the flame detection system.
According to a preferred embodiment of the invention, in fact, after the control for the closing of the check valve is given, the main power supply remains still active for all the burner circuits, for a preset period of time in which the flame detector can turn off the power to itself and to the pump motor, since the flame should extinguish out of fuel lack.
If, after a predetermined period of time has passed, the flame detector keeps revealing flame presence, that could mean that:

either the fuel detector has failed;
or the flame detector has failed.

In this case, according to the invention, the burner comes into a blocked status and cannot be restarted either automatically by the thermostats or manually, if not a previous check of good operation of the parts is performed.
In fact, this would reveal that the fuel valve has not closed and that it is out of order.
Further characteristics and peculiarities of the invention will be better explained in the description of a preferred embodiment of the logic circuit which realizes the improvement device according to the invention. The description is given by way of illustration only, whereby:

Fig.1 shows the operating phases of a burner according to the improvements of the control and monitoring circuit of the burner according to the invention;
Fig.2 shows an electric circuit which is apt to realize the operating cycle of Fig.1.

With reference to Fig.1, where the operation phases of the burner according to the invention are pointed out, it can be seen that, when the regulation thermostat closes (see the A-B segment), the electrofan of the burner is connected to power supply and also the fuel pump starts operation, since it is coaxial with the electrofan. In any case, the fuel cannot flow out, because the check valve is now closed.
At the same time, the photoresistance adjusted for high sensitivity detects if there are sources of external light. If this detection gives a negative result, i.e if there is not external light, at the time T1 the ignition transformer is powered and, simultaneously, the check valve opens. By feeding the ignition transformer, a spark is generated which lights the flame, and the burner begins to operate in the C-D segment.
In case the flame should extinguish, as can be seen in the D-E segment, then a new starting cycle is made, with the phases of checking for external light already seen in the A-B segment; then at E point, the ignition transformer is powered again and the fuel check valve consequently opens. If there is not any flame yet, as can be seen in the E-F segment, then at the time T3 the thermal relay indicated with TBB stops the operation of the burner. After the control and monitoring circuit of the burner has been manually released, a new starting is made in G-H as in A-B with the detection of the external light. In the H-T segment, as in B-C, the circuit of the ignition transformer closes again and the fuel feeding valve opens. In case the flame absence should persist, the TBB relay which stops the burner in absence of light, stops the circuit again.
In normal trouble-free operation, the control and monitoring cycle of the burner according to the invention is indicated in the A', B', C', D', K' segment, which is described hereinafter.
In the A'-B' segment, the closing of both the regulation thermostat causes the starting of the motor which drives the fan and the pump, and operates the external light detection circuit. If the detection is negative, the ignition transformer is closed in the B'-C' segment and, simultaneously, the check valve is opened so that the fuel which is already at pressure in the pump goes into the combustion chamber. In the C'-D' segment the flame is on, the check valve is open and the burner operates as requested. At the D' point, when the thermostat reaches the ambient temperature, the check valve is closed, while the motor stays on and so does the pump, since all the circuits of the burner remain powered. The flame can burn in the D'-K' segment until the fuel exhaustion, if there is still fuel in the combustion chamber of the burner.
So, there is a time indicated with T4 when the burner stops, while the check valve of the fuel feeder is closed, since the monitoring circuit of the burner is on if the flame extinguishes out of fuel lack. After the T4 time has passed, if the photoelectric cell still detects the flame presence, that is a proof that the check valve is defective and that is why the fuel has continued flowing out. After the T4 time, therefore, the circuit disconnects all the burner circuits from the power supply and, at the same time, causes the excitation of a lock relay TBL which is different from the lock relay TBB.
The lock caused by the lock relay TBL cannot be reset by the user; this is due to safety reasons, since the lock indicates that the check valve of the burner is defective. Therefore, in the realization according to the invention, the reset of the circuit in order to remove the lock caused by the solenoid valve TBL cannot be performed by the user, but only by qualified service personnel.
If the flame persists in the D'-K' segment, the fan keeps running, so that the fuel which comes out of the check valve, which either closes late or remains open because it is defective, burns.
Therefore, it is well understood that with the working cycle according to the invention and with the circuit which realizes it, the purpose is reached to overcome the disadvantages which the traditional burners present.
It should be pointed out that by preventing the unburnt liquid from dropping into the burner, the maximum cleanness of the burner is guaranteed, thus avoiding undesirable stops caused by dirtiness and also guaranteeing better thermal exchange between the flame and the boiler water; this allows a better efficiency of the whole heating cycle.
In Fig. 2 a description of the circuit which realizes the invention is shown. In detail, it can be observed that when IG, TA and TC are closed, the remote control relay 10 is excited which generates a signal 100. The signal 100 divides into two different paths which are indicated with 101 and 102. The signal 102, through the circuit section 1, commutates the contact C3 from A to B, so as to enable the signal to passage in the solenoid valve EV, though this passage does not take place because the switch C4 is still open.
The signal 101 causes the closing of the contact C5, through which the relay 20 is excited, since the contacts C2L and C8 are normally closed. The signals 201 and 202, which are generated by the closing of relay 20, cause the contact C9 and C10 to close. If the thermal block contact C1B is in its normal, i.e. closed, position, the motor M indicated with 30 is fed and it operates both the fan and the pump of the burner, which are coaxially connected to the motor shaft.
Feeding the motor 30 generates a low-voltage signal 301 in a secondary circuit of the motor stator; the signal feeds the block 40, which is the logic control and monitoring feeding circuit of the burner. The feeder 40 generates two correlated signals 401 and 402. The signal 401 feeds the amplifier 50, which in turn feeds the photoresistance FT of the external light control, during the burner pre-ventilation phase, and of the flame control (with a switched sensisivity) during the normal working of the burner. The same signal 401 reaches the transformer 70, which generates an ignition spark when the contact C11 is closed. This happens after a pre-ventilation time determined by the timer 60. The high-frequency transformer 70 is fed by the signal 402 coming from the feeder 40.
At the beginning of the fan operation cycle, with both the motor 30 and the blocks 40 and 50 on, the photoelectric cell FT, if it does not detect the presence of light, permits the block 50 to emit a signal 502. The signal 502 activates the timer block 60. After a time T1 has passed, the timer block 60 closes the contact C11 and the contact C4. The contact C11 permits the signal 401 to pass and to control the high tension transformer 70 and the emission of the ignition spark. The contact C4, which is closed, makes the solenoid valve EV open the fuel check valve.
If the photoelectric cell FT continues detecting the light absence, i.e. if the flame does not take fire, then the pick-up current IEV of the valve EV passes through TBB and the current intensity heats the resistance TBB so much as to open the block contact C1B through the connection 3. The opening of a block contact C1B disconnects the power from the motor and from the whole circuit, blocking the burner and lighting the pilot light. The block can be reset by closing the contact C1B manually.
But, if the flame is regular, the photoelectric cell FT detects light presence since the signal 502 is lacking, the contacts C4 and C11 are opened and so power is disconnected from the transformer 70 and from the resistance TBB, while the solenoid valve EV keeps on being excited through holding current.
When the regulation thermostat TA opens because the wanted temperature has been reached, the power is disconnected from the remote control relay 10, and consequently the contact C5 is opened, but the relay 20 is still on thanks to a self-holding contact. Therefore, the contact C9 remains closed and so does the contact C10, so that the motor 30, the block 40 and the block 50 are powered and, in turn, also the electrofan, the pump and the photoresistance. But, since the signal 100 is absent, the contact C3 returns to its normal position A, so that the signal 401 now passes through the resistance TBL and does not supply power to the solenoid valve any more.
Thus, the operation condition of the circuit according to the invention is reached, i.e. all the command and monitoring organs of the burner are powered, with the exception of the check solenoid valve of the fuel.
If everything is in order, the flame extinguishes and the photoelectric cell detects light absence. Consequently, the amplifier block 50 emits a signal 503, which permits the small current passing through TBL to close through the amplifier 50 in M. Therefore, all the available tension concentrates at the ends HK of the relay 80, so that the relay 80 excites and the contact C8 opens through the path 4. When the contact C8 opens, the relay 20 drops out. Consequently, the contacts C9 and C10 open, putting the circuit in the status of standstill burner , that is in the condition prior to the closing of the regulation thermostat. But, if the fuel flow does not stop after the regulation thermostat Ta has opened, then the photoresistance FT continues detecting the flame light and the current through TBL does not close in M through the amplifier any more, but it passes through the resistance with a high intensity, warming up to such an extent that it makes the contacts C2L open through the path 5.
This block contact C2L is positioned in the circuit in such a way that the latter can be reset only by qualified service personnel.
This because of clear safety reasons, since if the flame persists after the fuel valve has been closed, this means that the valve has not realized the closing.

Claims

A burner fitted with a control and monitoring circuit controlled by the regulation thermostat, comprising:
- at least one remote control device (10), connected with the regulation thermostat (Ta), which starts the burner electrofan which is coaxial with the fuel pump;

- one or more electric circuits (FT) components which detect the flame presence in the boiler;

- at least one valve for the fuel flow interception of the fuel feeding pump,
characterized in that the opening of the regulation thermostat (Ta) causes only the closing of the check valve of the fuel feeding, while the fan, the pump and the flame control device remain on and powered until either the flame or the simulation flame due to induced light is present.
A burner fitted with a control circuit according to claim 1), characterized in that a thermistor (TBL) connected with a normally closed blocking contact (C2L) disconnecting the power from all the burner circuits when the valve (EV) drops out, is passed through a current having such an intensity as to open the control and monitoring circuit of the burner.
A burner fitted with a control circuit according to claim 2), characterized in that, when there is flame presence or simulation presence, the blocking contact. (C2L) which is opened because of the prolonged flame presence after the time (T4) has passed from the closing of the valve for the fuel interception, is different from the blocking contact (C1B) which opens because of flame absence.